The radio transmission of communications signals, for example, audio signals, is normally effected by one of two methods. In one, referred to as an amplitude modulation system, a sinussoidal radio frequency carrier is modulated in amplitude in terms of the intelligence or communications signal, and when the signal is received at a receiving location, the reverse process, that is, demodulation of the carrier, is effected to recover the communications signal. The other system employs what is termed frequency modulation, and instead of amplitude modulation of the carrier signal, it is frequency modulated. When an FM frequency modulation or FM signal is received, circuitry is employed which performs what is termed discrimination wherein changes in frequency are changed to changes in amplitude in accordance with the original modulation, and thereby a communications signal is recovered. In both systems, there is as a basis a sinusoidal carrier which is assigned and occupies a distinctive frequency band width, or channel, and this channel occupies sprectrum space which cannot be utilized by other transmissions within the range of its employment. At this time, almost every nook and cranny of spectrum space is being utilized, and there is a tremendous need for some method of expanding the availability of communications channels. In consideration of this, it has been suggested that instead of the use of discrete frequency channels for radio communications links, which is the conventional approach, a radio transmission link employing a wider frequency spectrum which may extend over a range of 10 to 100 times the intelligence band width being transmitted, but wherein the energy of any single frequency making up that spectrum be very low, typically below normal noise levels. Thus, it would be obvious that this type of transmission would be essentially non-interfering with other services.
Additionally, and as well expressed in an article entitled "Time Domain Electromagnetics and Its Application," Proceedings of the IEEE, Vol. 66, No. 3, (March 1978), it has been suggested that baseband signals generated from pulses of a short duration, e.g., in the pico second range employed for such applications as baseband radar. Ranges on the order of 5 to 5,000 feet were suggested. This article appeared in 1978, and recent discussions with radar engineers as to subsequent development of baseband radar suggest that little has been achieved, particularly in the development of the widely use medium range field of up to 10 kilometers. The reasons given for the lack of success in this area appear to be signal reception from such systems cannot adequately combat noise. It is to be kept in mind that the signal-to-noise ratio problem is made enormous by the fact that the baseband radar signal received must compete with all of the electromagnetic noise occurring within the entire spectrum of the band of the radar signal, which is, for example, from 100 MHz to 1.5 GHz, or higher. Even where there is no intentional jamming of energy present, there is an enormous amount of electromagnetic energy present in addition to the poor radar signal at the input of a BAR BAseband Radar. On its face, the problem seems rather hopeless, and it is believed that this is about where the problem lies.